For decades, scientists have been searching for 'glueballs' – a mysterious particle that is vital to the workings of the standard model of physics.

A glueball is thought to be made up entirely of gluons, which are the 'sticky' particles that keep nuclear particles together.

In other words, they are particles created purely from force.

But because they are so unstable, glueballs can only be detected by studying their decay – and so far, no one has been able to spot this process in action.

Nucleons consist (left) of quarks (matter particles) and gluons (force particles). A glueball (right) is made up purely of gluons. For decades, scientists have been searching for so-called 'glueballs – a mysterious particle that is vital to the workings of the standard model of physics. Now researchers believe they may have found it

WHAT IS THE STANDARD MODEL?

For everything in the universe besides gravity, we have the 'Standard Model of Particle Physics' to explain what happens in our world.

The Standard Model describes how everything in the universe is made from a few basic building blocks called fundamental particles, which are governed by four forces.

These forces are gravity, electromagnetic, weak nuclear and strong nuclear.

The forces work over different ranges and have different strengths.

While the standard model has been shown to be true in various scenarios, it can't explain a number of forces in the world.

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Several particles have been found in particle accelerator experiments which are considered to be viable candidates for glueballs.

But there has never been a scientific consensus on whether or not one of these signals could in fact be the mysterious particle made of pure force.

Up until now, these alternative glueball decays have not been measured, but within the next few months, two experiments at the Large Hadron Collider at CERN (pictured) and one accelerator experiment in Beijing (BESIII) are expected to provide new data

'Simplified model calculations have shown that there are two realistic candidates for glueballs: the mesons called f0(1500) and f0(1710).'

WHAT ARE GLUEBALLS?

A glueball is thought to be made up entirely of gluons, which are the 'sticky' particles that keep nuclear particles together.

In other words, they are particles created purely from force.

Gluons can be seen as more complicated versions of the photon.

The massless photons are responsible for the forces of electromagnetism, while eight different kinds of gluons play a similar role for the strong nuclear force.

However, there is one important difference: gluons themselves are subject to their own force.

This is why there are no bound states of photons, but a particle that consists only of bound gluons, of pure nuclear force, is theoretically possible.

Because they are so unstable, glueballs can only be detected by studying their decay – and so far, no one has been able to spot this process in action

A meson is a subatomic particle composed of one quark and one antiquark.

'For a long time, the former was considered to be the most promising candidate,' said Rebhan.

'The latter has a higher mass, which agrees better with computer simulations, but when it decays, it produces many heavy quarks (the so-called 'strange quarks').

'To many particle scientists, this seemed implausible, because gluon interactions do not usually differentiate between heavier and lighter quarks.

But the latest study found that it is possible for glueballs to decay predominantly into strange quarks.

Surprisingly, the calculated decay pattern into two lighter particles agrees extremely well with the decay pattern measured for f0(1710).

Up until now, these alternative glueball decays have not been measured, but within the next few months, two experiments at the Large Hadron Collider at CERN (TOTEM and LHCb) and one accelerator experiment in Beijing (BESIII) are expected to yield new data.

'These results will be crucial for our theory', says Anton Rebhan. 'For these multi-particle processes, our theory predicts decay rates which are quite different from the predictions of other, simpler models.

'If the measurements agree with our calculations, this will be a remarkable success for our approach.'

It would be overwhelming evidence for f0(1710) being a glueball.

A confirmation of its existence would also once demonstrate that higher dimensional gravity research can be used to solve particle physics problems.

According to the researchers, this would provide more support for Einstein's theory of general relativity.